Coral Reefs

Coral Reefs
Marine Science
What are Coral Reefs?
 Coral Reefs are the
"Rainforests" of the ocean.
 Reefs are ecologically
important ecosystems and
have a high biodiversity that
serves as a storage bank of
rich genetic resources.
 They are a source of food
and medicine, and they
protect the coast from wave
erosion.
 Coral Reefs
The Organisms That Build Reefs
 Coral reefs are made of
vast amounts of calcium
carbonate (CaCO3),
limestone, that is
deposited by living things
 Corals: Structure and
Variety
Reef Corals
 Corals are cnidarians,
unlike many other
cnidarians, they lack a
medusa stage and live
only as polyps
 In reef-building corals the
polyps produce calcium
carbonate skeletons,
billions of these tiny
skeletons build a massive
reef
 Not all corals build reefs
The Coral Polyp
 Coral polyps are not only
small, but deceptively
simple in appearance,
they look much like little
sea anemones.
 They have an upright
cylinder of tissue with a
ring of tentacles on top,
 they use these stinging
tentacles to catch food,
especially zooplankton,
the tentacles surround the
mouth
The Coral Polyp
 A single founder polyp
lands somewhere on the
ocean floor and if it
survives, it divides over and
over to form the colony,
thus all polyps in a coral
colony are genetically
identical copies of the
founder polyp
 The digestive and nervous
systems of the polyps
remain connected
The Coral Polyp
 Nearly all reef-building
polyps contain symbiotic
zooxanthellae- a
dinoflagellate algae
 These zooxanthellae
provide coral with the
energy they need to
build their CaCO3
skeleton, without these
zooxanthellae there
would be no coral reefs
Coral Nutrition
 Zooxanthellae perform
photosynthesis and pass
some of the organic
matter they make onto
the coral
 Coral polyps are very
efficient at removing
zooplankton brought in by
currents therefore the
reefs have been called a
“wall of mouths”
Conditions for Reef Growth
 Reefs are rare on soft
bottoms because coral
larvae need to settle on a
hard surface
 Coral Reef Spawning
Light and Temperature
 Corals can only grow in
shallow water, where light
can penetrate, because the
zooxanthellae need the light
 Coral reefs are therefore
found only on continental
shelves, around islands or
on top of seamounts
 Corals also prefer clear
waters, so that light can get
through, and corals can
only reproduce is the
average water temperature
is above 68 F
 Where coral reefs are found
Light and Temperature
 If water to too warm,
corals will expel their
zooxanthellae, this is
called coral bleaching
because the corals turn
white without their
symbiotic zooxanthellae
 Widespread coral
bleaching occurs when El
Nino occurs, because it
brings warm water to
many parts of the ocean
 Global Warming
Sediments, Salinity, and Pollution
 Fine sediment, like silt, is
very harmful to corals, it
clouds the water
 To remove sediment,
corals slough off mucus,
which carries the
sediment off with it
 Coral Diseases
Fringing Reefs
 These are the most common
and simplest kind of reef
 Rocky shorelines provide the
best conditions for fringing
reefs, these reefs grow in a
narrow band or fringe along
the shore
 The longest reef in the world
is a fringing reef that runs
4000 km (2,500 mi) along the
coast of the Red Sea, the
climate is dry and no streams
bring in sediment or
freshwater
 Types of Reefs
Barrier Reefs
 Barrier reefs also lie
along the coast, but occur
considerably farther from
shore, occasionally as far
as 100 km (60 mi) or
more
 Barrier reefs are
separated from the shore
by a relatively deep
lagoon
Barrier Reefs
 The largest and most famous
barrier reef is the Great Barrier
Reef, it runs more than 2,000
km (1,200 mi) along the
northeastern coast of
Australia, it varies in width
between15 and 350 km (10
and 200 mi)
 The Great Barrier Reef is
actually a system of more than
2,500 smaller reefs and
lagoons
Atoll Structure
 An atoll is a ring of reef,
they can be found far
from land, rising up from
depths of thousands of
meters or more
 Atolls may be anywhere
from one mile across to
well over 20 miles
 Atolls may include a
dozen or more islands
and be home to
thousands of people
 Atoll are rings of reef,
with steep outer slopes,
that enclose a shallow
lagoon
How Atolls Grow
 An atoll begins as a
fringing reef around a
volcanic island, as the
island slowly sinks, the
reef flat gets wider and
deeper and eventually
becomes a lagoon, at this
stage the fringing reef
has become a barrier
reef, eventually the island
sinks altogether, leaving
only a ring of living
growing reef, an atoll
The Ecology of Coral Reefs
 Coral reefs are the
richest and most complex
of all marine ecosystems,
thousands of species
may live on a reef
 Coral Diversity
 Medicine from the Sea
Warm up
What are the three types of Reefs?
 What are some limiting factors for the
growth and reproduction of coral reefs?
Describe a coral polyp.
Why are Zooxanthellae important to corals?
The Trophic Structure of Coral Reefs
 Using sunlight,
zooxanthellae incorporate
nutrients into organic
compounds, which are
passed on to the coral
 The waste products of
fish can be an important
source of nutrients and
help the coral grow faster
 Seaweeds are an
important primary
producer on the reef, and
many fishes, sea urchins,
snails, and other animals
graze on these seaweeds
Competition
 Corals compete for the
space they need in many
ways, fast-growing ones
tend to grow upward and
then branch out, cutting their
neighbors off from light
 Other corals actually attack
their neighbors by digesting
the tissues of the other
corals or by stinging them
Predation on Corals
 A variety of animals eat
the corals, they keep the
reef in tact by just eating
individual polyps or bits
and pieces of the reef
 Ex. Parrotfish, Angelfish
The Crown-of-Thorn Sea Star
 The crown-of-thorns
feeds by pushing its
stomach out through the
mouth and digesting the
coral tissue with the
stomach
 Coral harbors symbiotic
crabs, shrimps, and other
fishes that discourage the
sea star predation by
pinching and biting their
tube feet
The Crown-of-Thorn Sea Star
 The crown-of-thorns sea
star has undergone
population explosions on
many Pacific reefs,
scientists are not sure
what, if anything, should
be done about this
Grazing
 Many fish,
especially parrotfishes
and damselfishes graze
intensively on reefs
 If these grazers are
removed, seaweeds can
flourish and take over
space from corals
 Many damselfishes act
as “farmers,” they pull out
unpalatable seaweeds
and remove them, and
what is left is a dense mat
of tasty seaweeds
Living Together
 Coral reefs probably have
more examples of
symbiosis than any other
biological community
 Symbiotic relationships
are very important in
coral reef communities
Saving coral reefs…
 Watch the following video clips and write a paragraph in
jour Journal on answering the following questions:
 Why are coral reefs important?
 What are reef balls?
 What are some ways of saving the coral reef?
 Do you think coral reefs should be saved?
 How can you help?
 Reef Balls
 Belize Coral Reef
 Electric Boost for Reefs
 Ocean-Saving Coral Reef
The End!
Thank you for your attention!